Galaxy’s centre tastes of raspberries and smells of rum, say astronomers
BY Ian Sample  /  21 April 2009

Astronomers searching for the building blocks of life in a giant dust cloud at the heart of the Milky Way have concluded that it tastes vaguely of raspberries. The unanticipated discovery follows years of work by astronomers who trained their 30m radio telescope on the enormous ball of dust and gas in the hope of spotting complex molecules that are vital for life. Finding amino acids in interstellar space is a Holy Grail for astrobiologists, as this would raise the possibility of life emerging on other planets after being seeded with the molecules.

In the latest survey, astronomers sifted through thousands of signals from Sagittarius B2, a vast dust cloud at the centre of our galaxy. While they failed to find evidence for amino acids, they did find a substance called ethyl formate, the chemical responsible for the flavour of raspberries. “It does happen to give raspberries their flavour, but there are many other molecules that are needed to make space raspberries,” Arnaud Belloche, an astronomer at the Max Planck Institute for Radio Astronomy in Bonn, told the Guardian. Curiously, ethyl formate has another distinguishing characteristic: it also smells of rum.

The astronomers used the IRAM telescope in Spain to analyse electromagnetic radiation emitted by a hot and dense region of Sagittarius B2 that surrounds a newborn star. Radiation from the star is absorbed by molecules floating around in the gas cloud, which is then re-emitted at different energies depending on the type of molecule. While scouring their data, the team also found evidence for the lethal chemical propyl cyanide in the same cloud. The two molecules are the largest yet discovered in deep space.

Dr Belloche and his colleague Robin Garrod at Cornell University in New York have collected nearly 4,000 distinct signals from the cloud but have only analysed around half of these. “So far we have identified around 50 molecules in our survey, and two of those had not been seen before,” said Belloche. The results are being presented today at the European Week of Astronomy and Space Science at the University of Hertfordshire.

Last year, the team came tantalisingly close to finding amino acids in space with the discovery of a molecule that can be used to make them, called amino acetonitrile. The latest discoveries have boosted the researchers’ morale because the molecules are as large as the simplest amino acid, glycine. Amino acids are the building blocks of proteins and are widely seen as being critical for complex life to exist anywhere in the universe. “I wouldn’t be surprised if we find an amino acid out there in the coming years,” said Belloche.

Previously, astronomers have detected a variety of large molecules, including alcohols, acids and chemicals called aldehydes. “The difficulty in searching for complex molecules is that the best astronomical sources contain so many different molecules that their ‘fingerprints’ overlap and are difficult to disentangle,” Belloche said. The molecules are thought to form when chemicals that already exist on some dust grains, such as ethanol, link together to make more complex chains. “There is no apparent limit to the size of molecules that can be formed by this process, so there’s good reason to expect even more complex organic molecules to be there,” said Garrod.

Arnaud Belloche
email : belloche [at] mpifr-bonn.mpg [dot] de

“In recent years, organic molecules of increasing complexity have been found toward the prolific Galactic center source Sagittarius B2. We wish to explore the degree of complexity that the interstellar chemistry can reach in star-forming regions. We carried out a complete line survey of the hot cores Sgr B2(N) and (M) with the IRAM 30 m telescope in the 3 mm range. We analyzed this spectral survey in the LTE approximation. We modeled the emission of all known molecules simultaneously, which allows us to search for less abundant, more complex molecules. We compared the derived column densities with the predictions of a coupled gas-phase and grain-surface chemical code. We report the first detection in space of ethyl formate (C2H5OCHO) and n-propyl cyanide (C3H7CN) toward Sgr B2(N). The abundances of ethyl formate and n-propyl cyanide relative to H2 are estimated to be 3.6e-9 and 1.0e-9, respectively. Our chemical modeling suggests that the sequential, piecewise construction of ethyl and n-propyl cyanide from their constituent functional groups on the grain surfaces is their most likely formation route. Ethyl formate is primarily formed on the grains by adding CH3 to functional-group radicals derived from methyl formate, although ethanol may also be a precursor. The detection in Sgr B2(N) of the next stage of complexity in two classes of complex molecule, esters and alkyl cyanides, suggests that greater complexity in other classes of molecule may be present in the interstellar medium.”

The giant molecular cloud, known as Sagittarius B2 (North), as seen by the NSF’s Very Large Array (VLA) radio telescope in New Mexico.

Complex organic molecules detected in interstellar space
BY John Matson / Apr 22, 2009

Two of the most complex molecules ever found outside the solar system have been turned up by astronomers peering into Sagittarius B2 (Sgr B2), a massive, vigorous star-forming region near the heart of the Milky Way.

Arnaud Belloche, an astronomer at the Max Planck Institute for Radio Astronomy in Bonn, Germany, and his colleagues detected the spectral signature of ethyl formate (far left in image) and n-propyl cyanide (at right in image) in electromagnetic radiation from Sgr B2. Both are relatively large organic (carbon-based) molecules—ethyl formate (C2H5OCHO) has 11 atoms and n-propyl cyanide (n-C3H7CN) has 12. Only cyanodecapentayne (HC11N), discovered in 1997, boasts more atoms among known interstellar molecules with 13.

Belloche and his co-authors suspect that the organics formed piecemeal on dust grains in the interstellar medium from pre-made building blocks. The mechanism could produce even more complex molecules, such as the amino acids that form proteins on Earth, but the signatures of such organics have yet to be found.

The researchers used the IRAM 30-meter telescope on Pico Veleta in southern Spain, near the city of Granada, which detects emissions in the millimeter regime—short-wavelength radio waves. Their results were presented this week at the European Week of Astronomy and Space Science at the University of Hertfordshire in England and are in press at the journal Astronomy & Astrophysics.

Sgr B2 has been a gold mine of organic compounds—the authors report that most complex molecules so far turned up in interstellar space were first discovered in a hot, dense cloud in the region called the “Large Molecule Heimat,” which is where the new research revealed ethyl formate and n-propyl cyanide.

In an interview with the Guardian, Belloche noted that ethyl formate is present in raspberries. The chemical “does happen to give raspberries their flavour,” Belloche told the newspaper, “but there are many other molecules that are needed to make space raspberries.” At the very least, perhaps ethyl formate makes space smell nice—according to the Occupational Safety and Health Administration, the chemical has “a pleasant, fruity odor.”

Highly complex organic molecules detected in space  /  4.21.2009

Scientists from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany, Cornell University, USA, and the University of Cologne, Germany, have detected two of the most complex molecules yet discovered in interstellar space: ethyl formate and n-propyl cyanide.

Their computational models of interstellar chemistry also indicate that even larger organic molecules may be present – including the so-far elusive amino acids, which are essential for organic life. The results will be presented at the European Week of Astronomy and Space Science at the University of Hertfordshire on Tuesday 21st April.

The IRAM 30 metre telescope in Spain was used to detect emissions from molecules in the star-forming region Sagittarius B2, close to the centre of our galaxy. The two new molecules were detected in a hot, dense cloud of gas known as the “Large Molecule Heimat”, which contains a luminous newly-formed star. Large organic molecules of many different sorts have been detected in this cloud in the past, including alcohols, aldehydes, and acids. The new molecules, ethyl formate (C2H5OCHO) and n-propyl cyanide (C3H7CN), represent two different classes of molecule – esters and alkyl cyanides – and they are the most complex of their kind yet detected in interstellar space.

Atoms and molecules emit radiation at very specific frequencies, which appear as characteristic “lines” in the electromagnetic spectrum of an astronomical source. Recognizing the signature of a molecule in that spectrum is rather like identifying a human fingerprint. “The difficulty in searching for complex molecules is that the best astronomical sources contain so many different molecules that their “fingerprints” overlap, and are difficult to disentangle” says Arnaud Belloche, scientist at the Max Planck Institute and first author of the research paper. “Larger molecules are even more difficult to identify because their ‘fingerprints’ are barely visible: their radiation is distributed over many more lines that are much weaker” adds Holger Müller, researcher at the University of Cologne. Out of 3700 spectral lines detected with the IRAM telescope, the team identified 36 lines belonging to the two new molecules.

The researchers then used a computational model to understand the chemical processes that allow these and other molecules to form in space. Chemical reactions can take place as the result of collisions between gaseous particles; but there are also small grains of dust suspended in the interstellar gas, and these grains can be used as landing sites for atoms to meet and react, producing molecules. As a result, the grains build up thick layers of ice, composed mainly of water, but also containing a number of basic organic molecules like methanol, the simplest alcohol.

“But,” says Robin Garrod, a researcher in astrochemistry at Cornell University, “the really large molecules don’t seem to build up this way, atom by atom.” Rather, the computational models suggest that the more complex molecules form section by section, using pre-formed building blocks that are provided by molecules, such as methanol, that are already present on the dust grains. The computational models show that these sections, or “functional groups”, can add together efficiently, building up a molecular “chain” in a series of short steps. The two newly-discovered molecules seem to have been produced in this way.

Garrod adds, “There is no apparent limit to the size of molecules that can be formed by this process – so there’s good reason to expect even more complex organic molecules to be there, if we can detect them.” Senior MPIfR team member Karl Menten thinks that this will happen in the near future: “What we are doing now is like searching for a needle in a haystack. Future instruments like the Atacama Large Millimeter Array will allow much more efficient studies to discover organic interstellar molecules.” These may even include amino acids, which are required for the production of proteins, and are therefore essential to life on Earth.

The simplest amino acid, glycine (NH2CH2COOH), has been searched for in the past, but has as yet not been successfully detected. However, the size and complexity of this molecule is matched by the two new molecules discovered by the team.

Star attraction
BY Marcus Chown / 27 November 1999

Forget the Restaurant at the End of the Universe – the Bar at the Centre of the Galaxy is where it’s at. At a conservative estimate, the gas cloud Sagittarius B2 contains 10^27 (that’s a billion billion billion) litres of alcohol at 200 per cent proof. Sadly, though, the alcohol is smeared throughout an enormous region of space in the form of a super-tenuous gas. To get enough to fill a whisky glass, you’d need to trawl a volume as big as the Earth itself.

Sagittarius B2 is a vast cloud 150 light years across lying within 400 light years of the giant black hole that lurks in the dark heart of the Milky Way. It is one of the biggest of the molecular clouds that account, collectively, for about 10 per cent of our Galaxy’s visible mass. And it’s a sobering (or not so sobering) thought that there is considerably more alcohol in a cloud like Sagittarius B2 than has been distilled in the entire history of the human race.

Twenty years ago, molecular clouds seemed little more than amorphous clumps of cold gas and dust floating between the stars. However, today’s high-resolution imaging has changed this picture. Molecular clouds turn out to be very complex. “If there is a typical one – and they are a very varied crowd – it consists of a relatively diffuse cloud of gas at about 20 degrees above absolute zero studded with hundreds of hotter, denser regions at about 200 to 400 kelvin,” says Lew Snyder, professor of astronomy and director of the Laboratory for Astronomical Imaging at the University of Illinois, Urbana-Champaign.

Dubbed “hot molecular cores”, the hot dense regions are stellar nurseries. They are also the places where molecules such as methyl alcohol (methanol) and ethyl alcohol (ethanol) are formed.

Chemistry in these clouds would be mind-bogglingly slow if it had to wait for the widely dispersed atoms or molecules flying through space to collide and stick together. However, the clouds also contain cold dust grains, usually made up of mantles of water ice and carbon compounds wrapped round silicon cores. The dust speeds things up by transforming chemistry from three dimensions to two. Molecular fragments collide and stick to the surfaces of the grains, then “migrate”, hopping around until they bump into a molecular mate. The energy to make the fragments hop comes from the grains, which are heated by newborn stars nearby.

Methanol and ethanol are among the 120 or so known interstellar molecules manufactured in this way. According to current ideas, they are created in one of two ways: they either form on grains of dust and then evaporate, or their components form on the grains and evaporate, and the final assembly takes place in space.

And it’s here, in space, that ethanol and methanol signal their presence. Both molecules rotate like tiny tops, but only at certain distinctive rates – an effect of quantum mechanics. Imagine a roundabout in a children’s playground that can only make a turn once a minute, twice a minute, three times a minute, and so on, but is forbidden to turn at any other rates. The rotation of molecules is restricted in a similar way.

If a molecule of alcohol collides with another molecule – say, of hydrogen, which is the most common molecule in space – the sudden jolt of energy can cause its spin rate to jump from one value to another. When the molecule relaxes back to a slower spin rate, it sheds the excess energy in the form of a photon with a wavelength in the centimetre or millimetre range.

Since different molecules radiate at characteristic wavelengths, astronomers have a foolproof means of distinguishing them. The great thing about light in the millimetre and centimetre region of the spectrum is that it easily penetrates the chokingly thick gas and dust in molecular clouds, providing a unique window into regions of star formation.

Methanol emits light at a wavelength of about 30 centimetres. It was first detected in 1970 when John Ball, Carl Gottlieb and A. E. Lilly of the Harvard-Smithsonian Center for Astrophysics found it in both Sagittarius B2 and a nearby cloud, Sagittarius A. Ethanol, on the other hand, emits light at about 3 millimetres. It was discovered in 1975 by a team led by Ben Zuckerman, then at the University of Maryland, using the 36-foot National Radio Astronomy Observatory dish at Kitt Peak in Arizona. The ethanol found by Zuckerman’s team was trans-ethanol, one of the two possible conformations of the molecule. The other, gauche-ethanol, was finally spotted in 1997 by John Pearson of the Jet Propulsion Laboratory in Pasadena.

Alcohols are also highly concentrated within molecular clouds – perhaps even more so than we realise. Unless astronomers can pick out the more concentrated clumps in the clouds, they tend to assume that alcohols are evenly spread. But it’s possible that there are many clumps that are too small to be resolved by current millimetre-wave telescopes. If so, says Snyder, we could be underestimating the concentration of the alcohol. It could even be 1000 times more concentrated than we think it is.

In common with other interstellar molecules, alcohols have a key role to play in star formation. A star is born when gravity causes a cloud of interstellar gas to collapse. However, even the meagre heat in these clumps of cold gas can generate enough pressure pushing outwards to oppose gravity. But the energy radiated by molecules saps molecular clouds of their heat, enabling gravity to gain the upper hand and start the collapse that leads to star birth.

But while alcohol was obviously important in the birth of the Sun and Earth, the story doesn’t end there. Alcohol is common not only in interstellar space but also in comets, the icy debris left over from the formation of the Solar System 4.6 billion years ago. There was rather a lot of it, for instance, in Comet Hale-Bopp.

The comet connection isn’t very surprising. Comets, like the Sun, congealed out of a long-dead molecular cloud. Scientists believe that cometary collisions with the newborn Earth supplied the planet with many of the molecules necessary to jump-start biochemistry – and alcohols are a prime example. They may well have helped to form the large molecular chains that life needed, says Snyder. “We suspect that alcohols from space played a key role in getting to amino acids like glycine and alanine.” If he’s right, alcohol could lie at the root of all life. That’s something to think about, next time you’re raising your glass.